This is very cool: seismometers deployed across the United States detected the seismic waves from the magnitude 5.9 earthquake that hit Virginia on August 23, 2011. In this animation showing the data you can actually see the wave rippling across the country!
What you’re seeing here are vertical displacement measurements from an array of detectors that are part of the USArray/EarthScope facility (you can read more about the array and the animation on the IRIS website). These are very sensitive instruments; note the scale on the lower graph showing the motion is only about 40 microns top-to-bottom! That’s less than the thickness of a human hair.
Red dots represent upward motion, and blue downward. The intensity of the color represents the amplitude (height) of the wave. Animations like this make it very easy to see the waves moving across the country; the arc even gives you a rough idea of where the epicenter was.
I grew up in Virginia, and went to UVa not far from the quake’s epicenter of Mineral, Virginia. I felt several earthquakes when I lived in California, and ironically there was a moderate quake about 360 km south of me in Colorado last night, but I never felt it! The Virginia quake, though, was felt as far away as Canada, apparently due to the East coast’s different crust structure than on the West coast, where quakes aren’t felt so far away. I didn’t know that, and that’s pretty interesting. Every state in the US has earthquakes, but the East coast quakes can be particularly dangerous because structures like houses and buildings aren’t built to withstand them. Perhaps this quake will be a wake-up call to construction companies and the government which regulates the industry.
I expect over the next day or two we’ll see psychics and people peddling earthquake prediction services to be chattering about this. However, there’s no way known to predict an earthquake, so if someone says they knew this was coming, well, go find a big ol’ grain of salt. And this quake (and the one in Colorado) has nothing to do with the Moon (which was full well over a week ago) or Comet Elenin or anything like that. The Earth is a tectonically active body, with a crust that sometimes lets us know that vast and powerful forces lurk beneath the surface. I think the scientifically reality of that knowledge — plus our ability to understand it, using measurements like the one in that video — is more than cool enough without having to make stuff up about it.
Credit: Data from the TA network were made freely available as part of the EarthScope USArray facility supported by the National Science Foundation, Major Research Facility program under Cooperative Agreement EAR-0350030. Tip o’ the tectonic plate to Emily Lakdawalla.